The shelf-life of silver halide elements can be seriously jeopardized by the action of cyanide under ambient conditions. That is, if a film generates cyanide or comes into contact with cyanide on standing, significant film fogging may occur. For this reason, cyanide scavengers are routinely coated into photographic films. The use of palladium in photographic elements to protect the elements from fog formation caused by hydrogen cyanide generated by carbon black has been described in U.S. Pat. 4,892,808. European Patent Application 0 597 312 A1 describes the use of palladium compounds in photographic elements to protect the elements from fog formation caused by hydrogen cyanide generated by chlorinated s-triazine hardeners and photographically useful chemical compounds containing cyano groups. The use of palladium or platinum containing compounds in photographic elements as a means of protecting the elements from fog formation has also been described in U.S. Pat. Nos. 2,552,229; 2,566,245 and 2,472,627.
With the current invention it has been discovered that fog can also occur during the processing of silver halide photographic elements due to the undesired presence of cyanide ion in the developing solution. The cyanide concentration in developing solutions varies from lab to lab and process to process, and the investigations of the present inventors have shown that levels in excess of 10 micromolar are not unusual in Process C-41 developer. Although the levels observed in the trade certainly present no health concern, this amount of cyanide can cause significant fogging in some photographic films.
There are numerous potential sources of cyanide in a photoprocessing environment. One source is the photographic element itself. Cyanide can be released by the thermal decomposition of triazine compounds and cyano-containing compounds which include many dyes, ultraviolet absorbers, couplers and polymerization initiators; materials that are often found in conventional silver halide photographic elements. The cyanide entrained in the photographic element can be released upon contact with developer and can build up in the developer, a process known as seasoning. It is also possible that some of the cyano-containing compounds coated in the photographic elements can react in developer solutions to yield cyanide. Alternatively, the developer may be contaminated by the local environment or other processing solutions. Cyanide can be generated by photochemical decomposition of ferricyanide (common photographic bleach), by oxidation of thiocyanate (common fix accelerator), and by reaction of hydroxylamine (common developer stabilizer) with formaldehyde (a common image stabilizer). Cyanide also can be found in carbon black materials (commonly used for film antihalation), polyurethanes, paper materials, and biocides. Cyanide is often used in high concentrations in the electrochemical plating of precious metals such as silver.
It has been found by the present inventors that while coated scavengers in a sensitized silver halide element are effective at scavenging cyanide in the ambient environment, they do not provide sufficient protection from cyanide which is present-in photographic developer solutions. Increasing the amount of scavenger coated in the photographic element is generally ineffective at preventing the fog generated by cyanide in developer. Further, it is not always an option to coat more scavenger due to various sensitometric consequences in the photographic element. The small amounts of a coated cyanide scavenger which may unintentionally season out of a photographic element are often insufficient to prevent fogging caused by cyanide in the developer.
Therefore, a need exists for a method of protecting photographic elements from fog generated by cyanide in the photographic developer which is simple and effective and which does not have a detrimental effect on the sensitometry of the photographic element.